The present invention relates to an endoceliac physical quantity measuring apparatus for detecting a change in a resonance state caused when an organic tissue as an object of measurement is touched by a body vibrating in a resonant state, and for determining physical quantities of the tissue based on the change.
Endoceliac physical quantity measuring apparatuses are described in, for example, Jpn. Pat. Appln. KOKOKU Publication No. 40-27236, Jpn. Pat. Appln. KOKAI Publication Nos. 1-189583 and 2-290529, etc.
In these conventional measuring apparatuses, a vibration system that includes a contact to be made to touch an organic tissue and a vibrator connected mechanically to the contact is caused to resonate by means of a self-oscillation circuit based on a feedback loop. The impedance of the organic tissue obtained when the tissue is touched by the vibrator or contact is grasped as a change in the oscillation frequency of the self-oscillation circuit or a change in voltage, whereby information on physical quantities of the tissue is obtained. Parameters associated with the physical quantities include elasticity, density, viscosity, etc.
The apparatus described in Jpn. Pat. Appln. KOKOKU Publication No. 40-27236 further comprises a horn member, which is located between the vibrator and the contact in order to magnify a vibrating amplitude. Also described in this publication is an apparatus that measures the softness of a substance at the distal end of a metal needle, especially an organic tissue, in the following manner. Ultrasonic vibration energy from an ultrasonic oscillator is given to the metal needle through an electroacoustic transducer, a change in mechanical load compared with ultrasonic vibration at the distal end of the needle is fetched as a change in the acoustic impedance of the transducer, and the change in the acoustic impedance is measured.
Another endoceliac physical quantity measuring apparatus is described in Jpn. Pat. Appln. Publication No. 7-241869. In this apparatus, a piezoelectric vibrator having a contact to be caused to touch an organic tissue is provided with an exciting electrode and a feedback electrode. The vibrator is caused to resonate by returning an output from the feedback electrode to the exciting electrode through a band-pass filter that has a band-pass frequency lower than the resonance frequency of the vibrator with the organic tissue untouched, or in unloaded state. Then, physical quantities of the organic tissue are obtained by detecting a change in the resonance frequency caused when the tissue is touched by the contact. When the contact touches a soft object such as an organic tissue, in general, the impedance of the vibrator increases with its resonance frequency going down, so that the output of the feedback electrode lowers. The band-pass filter passes the lowered frequency output from the feedback electrode with quarter amplitude, so that the voltage returned to the exciting electrode increases. Thus, the resonant state of the vibrator can be maintained despite the increase of the impedance, so that the physical quantities can be measured covering a wide range. The physical quantities of the organic tissue can be also obtained by detecting a change in the voltage applied to the exciting electrode.
According to the conventional endoceliac physical quantity measuring apparatuses, moreover, the vibration system that includes the vibrator to be made to touch an organic tissue is formed from a metallic material adapted for high acoustic velocity, in order to enhance the effect of vibration transmission. Also, a casing member covering the vibration system is supported by means of an elastic member so that vibration is prevented from being transmitted to the casing member.
These endoceliac physical quantity measuring apparatuses have advantages in enjoying quantitative measurement of physical quantities of organic tissues by means of a non-destructive electrical measurement that requires only a short time. On account of these advantages, the apparatuses of this type are expected to be used as tactile sensors for the measurement of the elasticity of the human body's skin or for industrial robots.
According to the conventional endoceliac physical quantity measuring apparatuses, however, a physical quantity of an organic tissue obtained when the tissue is touched by the piezoelectric vibrator or the contact connected mechanically thereto is grasped as a change in the oscillation frequency of the self-oscillation circuit or a change in voltage, whereby information on the physical quantity of the tissue is obtained. In detecting differences between physical quantities of a soft object such as an organic tissue, especially a very soft internal tissue such as the inner wall of the stomach or esophagus, therefore, the resolution is so low that measurement data are subject to substantial dispersion. Further, the outputs of the measuring apparatuses are influenced considerably by the contact load between the organic tissue and the contact, so that the accuracy of the measurement is lowered.
For example, the amplitude of a feedback signal from the feedback electrode of the apparatus described in Jpn. Pat. Appln. Publication No. 7-241869 is subject to the influence of dispersion according to individual vibrators. In detecting the change of the voltage applied to the exciting electrode, moreover, the bandpass filter's Q-factor must be high enough to allow the reduced amplitude of the feedback signal to be augmented by increasing the gain. In consequence, it is difficult to adjust the respective frequency characteristics of the band-pass filter and the piezoelectric vibrator to one another.
In the prior art endoceliac physical quantity measuring apparatuses described above, furthermore, the impedance of the organic tissue as the object of measurement is considerably lower than the vibration energy of the vibrator, so that the variation of the oscillation frequency or voltage caused as the tissue is touched by the vibrator is much smaller than that obtained before the touch. Technically, therefore, it is very difficult to fetch electrically the variation of the oscillation frequency or voltage that is attributable to the touch on the organic tissue. Even if the variation can be fetched, the resulting data includes a lot of noises and lacks reliability. In general, for these reasons, it is hard to make high-accuracy measurements using these conventional measuring apparatuses
In the above described measuring apparatus that has the horn member interposed between the vibrator and the contact to augment the amplitude of vibration of the contact, to thereby ensure high-accuracy measurements, the vibrator, horn member, and contact are arranged in a straight line. Accordingly, the apparatus has so long an overall length that its operability is poor, and requires use of many components that result in a high cost.
According to the conventional endoceliac physical quantity measuring apparatuses, moreover, the casing member that covers the vibration system is supported by means of the elastic member, so that the apparatuses have problems including complicated construction, low assembly performance, and poor operability attributable to its large outside diameter. In the case the apparatus is inserted into a patient's body through an endoscope to measure physical quantities of an organic tissue for diagnostic purposes, in particular, the endoscope used is expected to have a large diameter, which inevitably inflicts pain on the patient.
In the conventional endoceliac physical quantity measuring apparatuses described above, furthermore, the detected change of the impedance is greatly influenced by the load or angle of engagement under or at which the vibrator, for use as an electroacoustic transducer to be directly in touch with an organic tissue, or the contact, as a vibration transmitting member for guiding the vibration of the transducer to the tissue, touches the tissue.
Thus, accurate measurements of physical quantities require skilled operation. In the case where the object of measurement is a soft structure, such as an organic tissue, in particular, measurement data are subject to substantial dispersion, and it is very hard to make reliable measurements with high reproducibility.